METHOD FOR FABRICATING MEMS DEVICE
A method for fabricating MEMS device includes: providing a single crystal substrate, having first surface and second surface and having a MEMS region and an IC region; forming SCS mass blocks on the first surface in the MEMS region; forming a structural dielectric layer over the first surface of the substrate, wherein a dielectric member of the structural dielectric layer is filled in spaces surrounding the SCS mass blocks in the MEMS region, the IC region has a circuit structure with an interconnection structure formed in the structural dielectric layer; patterning the single crystal substrate by an etching process on the second surface to expose a portion of the dielectric member filled in the spaces surrounding the SCS mass blocks; performing isotropic etching process at least on the dielectric portion filled in the spaces surrounding the SCS mass blocks. The SCS mass blocks are exposed to release a MEMS structure.
Latest SOLID STATE SYSTEM CO., LTD. Patents:
- Structure of micro-electro-mechanical-system microphone and method for fabricating the same
- STRUCTURE OF MICRO-ELECTRO-MECHANICAL-SYSTEM MICROPHONE AND METHOD FOR FABRICATING THE SAME
- Structure of micro-electro-mechanical-system microphone and method for fabricating the same
- Structure of micro-electro-mechanical-system microphone
- Structure of micro-electro-mechanical-system microphone
1. Field of Invention
The present invention relates to microelectromechanical system (MEMS) device. More particularly, the present invention relates to a method for fabricating CMOS MEMS device having single crystal structure (SCS) for the MEMS structure.
2. Description of Related Art
MEMS device has been proposed in various applications. However, the MEMS device usually is staying in an open environment. Since the MEMS structure of the MEMS device is sensitive to the environmental air, the operation in open environment may pick up noise. A hermetic MEMS device is then proposed.
A hermetic MEMS package has properties including isolating the MEMS from the outside environment. For example, the damping of air and thermal noise can be avoided by forming a vacuum environment for MEMS. In addition, hermetic camber can protects the MEMS device from EM interference and produce a small size MEMS device with high performance and low cost for popularity. The applications for the hermetic MEMS packages include accelerometer, gyroscope, resonator, or RF MEMS components.
For the current hermetic MEMS products, the MEMS and sensing element are manufactured in separate substrate.
However, this conventional process has some drawbacks, including high cost, production yield issue due to three elements being packaged into a device, and parasitic effect for the conjunction of MEMS and sensing IC.
In addition to the hermetic chamber for MEMS device, the mechanical quality in MEMS structure is also important. For the current process with MEMS in integrated circuit(IC) substrate, the MEMS structure is usually formed by the metal layer and dielectric layer used in the interconnection of integrated circuits. However, the mechanical quality is unstable using the interconnection layers of CMOS as MEMS structures. For example, the residue stress may be different significantly within a single wafer or wafer by wafer.
When fabricating CMOS MEMS device having the single crystal structure, the fabrication needs to be further concerned and developed.
SUMMARY OF THE INVENTIONThe invention provides a method for fabricating a MEMS device. The MEMS device can be based on a single crystal structure (SCS).
In an aspect of the invention, a method for fabricating MEMS device includes providing a substrate, having a first surface and a second surface and having a MEMS region and an integrated-circuit (IC) region. Then, a plurality of SCS (single crystal structure) mass blocks are formed on the first surface of the substrate in the MEMS region. A structural dielectric layer is formed over the first surface of the substrate. The structural dielectric layer has a dielectric member. The spaces surrounding the SCS mass blocks in the MEMS region are filled with the dielectric member. The IC region has a circuit structure with the interconnection structure formed in the structural dielectric layer. An isotropic etching process is performed at least on the dielectric member filled in the spaces surrounding the mass blocks. Wherein, the mass blocks are exposed to release a MEMS structure.
In an aspect of the invention, a method for fabricating MEMS device, having a first surface and a second surface and having a MEMS region and an integrated-circuit (IC) region. Then a MEMS structure is formed over the first surface of the substrate. A structural dielectric layer is formed over the first surface of the substrate. The structural dielectric layer has a dielectric member and the spaces surrounding the MEMS structure is filled with the dielectric member. The substrate is patterned by an etching process from the second surface of the substrate to expose a portion of the dielectric member filled in the space surrounding the MEMS structure. A wettable thin layer is formed to cover an exposed portion of the substrate at the second surface. At least an etching process is performed on the dielectric member filled in the spaces surrounding the MEMS structure. The MEMS structure is exposed and released by the etching process, wherein the etching process comprises an isotropic etching process with a wet etchant and at least a portion of the dielectric member in the spaces surrounding the MEMS structure is removed by the said isotropic etching from the second side of the substrate.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
In the invention, several methods for fabricating MEMS device are proposed. The MEMS device is fabricated based on single crystal structure. Moreover, a MEMS having a hermetic chamber or a MEMS opening to the environment are also fabricated based on single crystal structure
Generally, the fabrication of SCS (single crystal structure) is used in fabrication for CMOS (complementary metal-oxide-semiconductor) integrated circuit. However, the MEMS device can be formed by the manner of SCS. The invention proposes a fabrication method for the MEMS device. Also and, the MEMS device is easy to be formed with an embedded hermetic chamber, according to several embodiments. Basically, for example, the SCS of MEMS device can be suspended from silicon substrate on the front side of the substrate. Alternatively, the SCS of MEMS device can be suspended from silicon substrate on the back side of the substrate. In addition, the extra electrode may be able to form on the side wall of SCS to increase the capacitance for MEMS capacitance sensing.
The MEMS device fabricated in SCS can have stable mechanical quality. The silicon wafer is well controlled during manufacturing. In addition, the MEMS device with hermetic chamber can isolate the MEMS structure from the interference of outside environment. Even further, a vacuum environment within the hermetic chamber can be formed for the MEMS device to avoid the interference of air damping and thermal noise of air. The MEMS device with hermetic chamber can have various applications, such as accelerometers, gyroscopes, resonator, switched, RF MEMS components, . . . , and so on.
Besides, for some MEMS exposed to the environment to sense acoustic signal or air pressure, e.g. MEMS microphone or pressure sensor, such MEMS structure is have one moveable diaphragm and a rigid back plate to form a capacitor for capacitance sensing. The back plate of the capacitor can be fabricated in the process of SCS while the moveable diaphragm is formed by conductive and dielectric layers used in the interconnection of CMOS circuit.
The release of MEMS structure with SCS manner in CMOS IC can be done by including several processes. For example, isotropic etching with wet or vapor etchant (Vapor HF) can be used to remove the dielectric layer surrounding the SCS. The CMOS circuits on the front side of the substrate are protected by a protection layer. The sealing structural dielectric layer covering the MEMS can protect the CMOS circuits from damage during the release. An oxide layer is deposited on the exposed silicon surface to lead the wet etchant to pass by the silicon holes, channels or cavity and reach the dielectric layer, such as silicon oxide, before performing wet isotropic etching process to release the MEMS.
Further, the embedded hermetic chamber for MEMS device can be achieved by forming a cover on the bottom of the substrate to form a hermetic chamber. The exposure of metal pad can be before or after the formation of the hermetic chamber.
Several embodiments are provided for describing the invention. However, the invention is not limited to the provided embodiments and the provided embodiments can be properly combined to each other.
In
In
In
In
In
In
In
In
In FIG. 3E(a), an etching back process is performed to remove the conductive layer 314. A residue portion of the conductive layer 314 becomes the spacer 314 on the sidewall of the trenches 310. FIG. 3E(b) is a top view, in which the cross-sectional view at cutting line I-I is like the structure in FIG. 3E(a). The dielectric layer 312 in the top view of FIG. 3E(b) is just showing the spacer portion. It can be seen that the substrate of the MEMS structure can be, for example, T shape viewed from the periphery. The suspension beam structure 321 is then formed while the end portion is serving as the anchor 323, so as to hold the suspension beam structure 321. However, it is not the only choice but depending on how the MEMS structure is designed. In other words, the MEMS structure on the substrate has a suspension beam structure with respect to the substrate.
In
In
In
In
Alternatively like in
The structural dielectric layer has seal the chamber from one side of the substrate. The MEMS structure is still embedded in the whole structure not being released yet.
In
In
However, the isotropic etching process can also be, for example, a wet etching. In
In
In
In
In
In
As described above, the MEMS structure can be formed in different process to have the desired structure. However, the fabrication principle is the same that the structural dielectric layer with the embedded structure, including conductive circuit structure and the mechanical strength structure layer at the MEMS region can be formed while the CMOS IC can be formed at the CMOS IC region. The conductive circuit structure may include capacitance and interconnect, for example. The CMOS IC region can be formed with the necessary CMOS IC. The structural dielectric layer is also seal the chamber from the top side.
In
In
In
In
In
In
After the MEMS structure is released and the chamber is formed, in which the front side has been sealed, another side of the chamber is to be sealed by packaging process.
In
In
In
In
In
In further applications, when the MEMS structure is used in the application of microphone, the fabrication processes can still be based on the same fabrication principle as previously described.
In
In
In the above etching process, due to the help of the silicon oxide layer 728, the isotropic etching process, such as the wet etching process, with the etchant can more easily enter the space 730 through the narrow venting holes. The etching stop layer 718 is also in use as a protection layer during etching process.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing descriptions, it is intended that the present invention covers modifications and variations of this invention if they fall within the scope of the following claims and their equivalents.
Claims
1. A method for fabricating micro electromechanical system (MEMS) device, comprising:
- providing a single crystal substrate, having a first surface and a second surface opposite to the first surface and having a MEMS region and an integrated-circuit (IC) region;
- forming a plurality of SCS (single crystal structure) mass blocks on the first surface of the substrate in the MEMS region;
- forming a structural dielectric layer over the first surface of the substrate, wherein the structural dielectric layer has a dielectric member and spaces surrounding the SCS mass blocks in the MEMS region are filled with the dielectric member, wherein the IC region has a circuit structure with an interconnection structure formed in the structural dielectric layer;
- patterning the single crystal substrate by an etching process on the second surface to expose a portion of the dielectric member filled in the spaces surrounding the SCS mass blocks; and
- performing an isotropic etching process at least on the dielectric member filled in the spaces surrounding the SCS mass blocks, wherein the SCS mass blocks are exposed to release a MEMS structure.
2. The method for fabricating MEMS device in claim 1, wherein the step of forming the mass blocks comprises:
- forming a first mask layer corresponding to the SCS mass blocks in an arbitrary shape on the first surface of the substrate, wherein the first mask layer has multiple first opening patterns at the MEMS region to expose the substrate;
- etching the substrate with the first mask layer as an etching mask to form a plurality of trenches at a depth to produce the SCS mass blocks with the arbitrary shape on the substrate;
- forming a dielectric spacer on a sidewall of the trenches and the first opening patterns of the first mask layer as a second mask; and
- performing an isotropic etching process with the first mask and the second mask to remove a portion of the substrate, wherein at least a portion of the SCS mass blocks is suspended with respect to the substrate to form a suspension beam structure in the SCS mass blocks, wherein a portion of the SCS mass blocks remains on the substrate.
3. The method for fabricating MEMS device in claim 2, the step of forming the dielectric spacer on the sidewall of the trenches comprises:
- forming a dielectric layer over the substrate in a conformal shape; and
- performing an etching back process on the dielectric layer, wherein a residue portion of the dielectric layer becomes the dielectric spacer.
4. The method for fabricating MEMS device in claim 2, wherein the trenches have a geometric shape in accordance with the intended MEMS structure.
5. The method for fabricating MEMS device in claim 1, wherein the step of forming the SCS mass blocks comprises:
- forming a first mask layer corresponding to the SCS mass blocks in an arbitrary shape on the first surface of the substrate, wherein the first mask layer has multiple first opening patterns at the MEMS region to expose the substrate;
- etching the substrate with the first mask layer as an etching mask to form a plurality of trenches at a depth to produce the SCS mass blocks of arbitrary shape;
- forming a sandwich spacer on a sidewall of the trenches as a second mask, wherein the sandwich spacer has a conductive spacer embedded in the dielectric spacer; and
- performing an isotropic etching process with the first mask and the second mask to remove a portion of the substrate, wherein at least a portion of the SCS mass blocks is suspended with respect to the substrate to form a suspension beam structure in the SCS mass blocks, wherein a portion of the SCS mass blocks remains on the substrate.
6. The method for fabricating MEMS device of claim 5, wherein the step of forming the sandwich spacer comprises:
- forming a dielectric over the substrate in a conformal shape;
- forming a conductive layer over the substrate in a conformal shape; and
- performing an etching back process on the conductive layer.
7. The method for fabricating MEMS device of claim 6, wherein after performing the etching back process, the conductive spacer remains on the sidewall of the trenches.
8. The method for fabricating MEMS device in claim 1, further comprising forming an wettable layer to cover an exposed portion of the substrate at the second surface before performing the isotropic etching process.
9. The method for fabricating MEMS device in claim 8, wherein the isotropic etching process is a wet etching process and has a wet etchant in the wet etching process, wherein the wettable layer is reactive with the wet etchant or the surface of the wettable layer is wetted by the wet etchant.
10. The method for fabricating MEMS device in claim 1, wherein the isotropic etching process comprises vapor etching.
11. The method for fabricating MEMS device in claim 1, wherein the step of patterning the single crystal substrate comprises:
- forming a hard mask layer on the second surface of the substrate;
- patterning the hard mask layer to have an opening to expose the substrate at the MEMS region;
- forming an etching mask layer on the hard mask layer and a portion of the substrate within the opening;
- performing a first anisotropic etching process on the substrate with the etching mask layer as a mask to expose a portion of the dielectric member in the structural dielectric layer;
- removing the etching mask layer;
- performing a second anisotropic etching process on the substrate with the hard mask layer as a mask, wherein the exposed portion of the substrate within the opening is removed by a portion to have a lower surface level.
12. The method for fabricating MEMS device in claim 1, wherein in the step of performing the isotropic etching process, all of the spaces are joined into a joined single space.
13. The method for fabricating MEMS device in claim 1, wherein in the step of patterning the single crystal substrate by the etching process on the second surface of the single crystal substrate comprising:
- forming an etching mask layer on the second surface of the substrate, wherein the etching mask layer has an opening at the MEMS region to expose the second surface of the substrate; and
- performing an anisotropic etching process on the substrate with the etching mask layer to expose the dielectric member filled in the spaces surrounding the SCS mass blocks.
14. The method for fabricating MEMS device in claim 1, wherein in the step of forming the structural dielectric layer, the structural dielectric layer over the first surface of the substrate comprises a mechanical strength structure layer capping over the mass blocks in the MEMS region,
- wherein in the step of performing the isotropic etching process, a portion of the dielectric member filled in the spaces surrounding the SCS mass blocks and under the mechanical strength structure layer is removed,
- wherein the mechanical strength structure layer and the mass blocks are exposed to release the MEMS structure, wherein the etched portions of the substrate, the portion of the dielectric member filled in the spaces surrounding the SCS mass blocks and under the mechanical strength structure layer forms a chamber.
15. The method for fabricating MEMS device in claim 14, further comprising a cover layer onto the substrate at the second surface of the single crystal substrate to cover the chamber, so as to form a hermetic chamber.
16. The method for fabricating MEMS device in claim 14, wherein the mechanical strength structure layer formed in the structural dielectric layer comprises a grid structure layer and a sidewall layer standing on the substrate.
17. The method for fabricating MEMS device in claim 14, wherein the mechanical strength structure layer formed in the structural dielectric layer comprises a plurality of conductive layers and a dielectric layer enclosed by the conductive layers.
18. The method for fabricating MEMS device in claim 1, wherein in the step of forming the structural dielectric layer, the structural dielectric layer over the first surface of the substrate comprises a diaphragm structure layer over the SCS mass blocks in the MEMS region,
- wherein in the step of performing the isotropic etching process, a portion of the dielectric member filled in the spaces surrounding the SCS mass blocks and on both sides of the diaphragm structure layer is removed to release the MEMS structure,
- wherein an end portion of the diaphragm remains in the structural dielectric layer and a center portion of the diaphragm is exposed,
- wherein the etched portions of the substrate, the portion of the dielectric member filled in the spaces surrounding the SCS mass blocks and under the diaphragm structure layer forms a chamber.
19. The method for fabricating MEMS device in claim 18, wherein the SCS mass blocks in the chamber are connected to form a SCS plate with a plurality of vent holes, wherein the vent holes connect a space under the diaphragm and a space produced by the etched portions of the substrate.
20. The method for fabricating MEMS device in claim 18, wherein the diaphragm structure layer comprises a corrugated dielectric layer enclosed by conductive layers.
21. The method for fabricating MEMS device in claim 1, wherein forming the SCS mass blocks comprises:
- forming a first mask layer corresponding to the SCS mass blocks with an arbitrary shape on the first surface of the substrate, wherein the first mask layer has multiple first opening patterns at the MEMS region to expose the substrate; and
- etching the substrate with the first mask layer as an etching mask to form a plurality of trenches at a depth to produce the SCS mass blocks with the arbitrary shape.
22. The method for fabricating MEMS device in claim 21, wherein a portion of the SCS mass block is suspended with respect to the substrate to form a suspended beam structure in the step of patterning the single crystal substrate by the etching process on the second surface, wherein a portion of the mass block remains on the substrate.
23. The method for fabricating MEMS device in claim 1, wherein the step of forming the SCS mass blocks comprises:
- forming a first mask layer corresponding to the SCS mass blocks with an arbitrary shape on the first surface of the substrate, wherein the first mask layer has multiple first opening patterns at the MEMS region to expose the substrate;
- etching the substrate with the first mask layer as an etching mask to form a plurality of trenches at a depth to produce the SCS mass blocks with the arbitrary shape;
- forming a dielectric layer on a sidewall of the trenches; and
- forming a plurality of conductive spacers on the dielectric layer; wherein the SCS mass blocks comprise the conductive spacers on the sidewall.
24. The method for fabricating MEMS device of claim 23, wherein the step of forming the conductive spacer comprises:
- forming a dielectric layer over the substrate in a conformal shape;
- forming a conductive layer over the substrate in a conformal shape; and
- performing an etching back process on the conductive layer, wherein a residue of the conductive layer forms the conductive spacer.
25. The method for fabricating MEMS device of claim 24, wherein after performing the etching back process, the conductive spacers remain on the sidewall of the trenches.
26. The method for fabricating MEMS device in claim 23, wherein a portion of the SCS mass blocks is suspended with respect to the substrate to form a suspended beam structure at the step of performing the etching process on the second surface of the single crystal substrate, wherein a portion of the SCS mass blocks remains on the substrate.
27. The method for fabricating MEMS device in claim 1, further comprising a protection stack layer, over the structural dielectric layer and an output pad structure of the circuit structure.
28. The method for fabricating MEMS device in claim 27, further comprising performing an etching back process on the protection stack layer to expose the output pad structure of the circuit structure in the structural dielectric layer.
29-33. (canceled)
Type: Application
Filed: Jan 22, 2010
Publication Date: Jul 28, 2011
Patent Grant number: 8030112
Applicant: SOLID STATE SYSTEM CO., LTD. (Hsinchu)
Inventors: Tsung-Min Hsieh (Taipei County), Chien-Hsing Lee (Hsinchu County), Jhyy-Cheng Liou (Hsinchu County)
Application Number: 12/691,754
International Classification: H01L 21/302 (20060101);